Basically a FET is a transistor having a source, a gate, and a drain. The action of the FET depends on the flow of majority carriers along a channel between the source and drain that runs past the gate. Current through the channel, which is between the source and drain, is controlled by the transverse electric field under the gate. More than one gate (multi-gate) can be used to more effectively control the channel. The length of the gate determines how fast the FET switches, and can be about the same as the length of the channel (i.e., the distance between the source and drain).
The size of FETs has been successfully reduced through the use of one or more fin-shaped channels. A FET employing such a channel structure can be referred to as a FinFET. Previously, complementary metal-oxide semiconductor (CMOS) devices were substantially planar along the surface of the semiconductor substrate, the exception being the FET gate that was disposed over the top of the channel. Fins break from this paradigm by using a vertical channel structure in order to maximize the surface area of the channel that is exposed to the gate. The gate controls the channel more strongly because it extends over more than one side (surface) of the channel. For example, the gate can enclose three surfaces of the three-dimensional channel, rather than being disposed only across the top surface of the traditional planar channel. In some devices the gate can completely enclose the channel, i.e., a suspended channel passes through the gate and all surfaces of the channel are exposed to the gate.
One challenge in fabricating multi-gate FETs is the inherently high parasitic capacitance as compared to conventional planar FETs. For example, reference can be made to “Simulation Study of Multiple FIN FinFET Device Design for 32 nm Technology Node and Beyond”; X. Wang et al., Simulation of Semiconductor Process and Device, Vol. 12, pages. 125-128, and to “Impact of Fringe Capacitance on Performance of Nanoscale FinFETs”, C. R. Manoj et al., IEEE Electron Device Letters, Vol. 31, p. 83-85.